JP2014043514A - PRODUCTION METHOD OF β TYPE POLYVINYLIDENE FLUORIDE FILM, β TYPE POLYVINYLIDENE FLUORIDE FILM, AND PIEZOELECTRIC TYPE SENSOR HAVING β TYPE POLYVINYLIDENE FLUORIDE FILM - Google Patents

Abstract

A method for producing a β-type polyvinylidene fluoride film having excellent piezoelectric characteristics and high purity that can be produced by a simple method without requiring large-scale equipment, a β-type polyvinylidene fluoride film, and a β-type polyvinylidene fluoride film are provided. A piezoelectric sensor is provided.
A method of manufacturing a β-type polyvinylidene fluoride film is obtained by mixing polyvinylidene fluoride, a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixing it to β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. Forming a coating solution, applying the obtained coating solution to a substrate to form a coating film, drying the coating film, and washing the dried film with water.
[Selection figure] None

Description

  The present invention relates to a method for manufacturing a β-type polyvinylidene fluoride film, a β-type polyvinylidene fluoride film, and a piezoelectric sensor including the β-type polyvinylidene fluoride film.

  Conventionally, polyvinylidene fluoride is known as a polymer piezoelectric material. This polyvinylidene fluoride has already been used as a piezoelectric material in various sensors such as hydrogen sensors, pressure sensors, ultrasonic sensors, acceleration sensors, and vibration sensors. In the future, information processing devices such as software, actuators, etc. Application to output devices is also expected.

  Polyvinylidene fluoride has three types of crystal structures, α-type, β-type, and γ-type. Among them, only the β-type has piezoelectricity. Such a β-type polyvinylidene fluoride film is usually uniaxially stretched with nonpolar α-type polyvinylidene fluoride in order to transfer the crystal structure from nonpolar α-type to polar β-type. It cannot be produced without polarization treatment. For this reason, the manufacture of a polyvinylidene fluoride film requires large-scale equipment such as a stretching machine and a polarization device (see, for example, Patent Document 1).

  Also proposed is a method for producing a piezoelectric body by melting and extruding α-type polyvinylidene fluoride without uniaxial stretching and performing only polarization treatment without changing the crystal structure from α-type to β-type. (For example, refer to Patent Document 2).

  However, even with such a manufacturing method, there is a problem that an extruder and a polarization device that applies a high electric field are required, and the manufacturing cost is high. In addition, from the viewpoint of reducing environmental burdens in recent years, there is a demand for a method for manufacturing a piezoelectric material that has few manufacturing steps and suppresses manufacturing costs.

  Further, it is known that an α-type, β-type, or a mixed type (γ-type) film can be formed by forming a polyvinylidene fluoride film together with a predetermined compound (see Non-Patent Documents 3 and 4). ), A high-purity polyvinylidene fluoride film cannot be formed.

JP 2011-006596 A JP2011-192665A

Journal of The Electrochemical Society, 153 (2) G119-G124 (2006) Macromolecules, Vol. 8, no. 2, March-April 1975 p158-p170

  In view of such circumstances, the present invention does not require large-scale equipment and is capable of being manufactured by a simple method with excellent piezoelectric characteristics and a high purity β-type polyvinylidene fluoride film, β-type polyvinylidene fluoride film, β An object of the present invention is to provide a piezoelectric sensor having a type of polyvinylidene fluoride film.

  An aspect of the present invention that solves the above-described problems is a method for producing a β-type polyvinylidene fluoride film, which is a polyvinylidene fluoride, a water-soluble polar solvent that dissolves the polyvinylidene fluoride and fixes it to β-type, and the water-soluble A step of mixing an organic solvent having a boiling point lower than that of the polar solvent to form a coating solution, a step of coating the obtained coating solution on a substrate to form a coating film, and a step of drying the coating film. And a step of washing the dried membrane with water, and a method for producing a β-type polyvinylidene fluoride membrane.

  According to this invention, a β-type polyvinylidene fluoride film having excellent piezoelectric characteristics and high purity can be produced by a simple method without requiring large-scale equipment.

  Here, the volume ratio of the water-soluble polar solvent and the organic solvent having a boiling point lower than that of the water-soluble polar solvent is preferably in the range of 1: 3 to 3: 1.

  According to this, a β-type polyvinylidene fluoride film having excellent piezoelectric characteristics and high purity can be produced by a simple method without requiring large-scale equipment.

  The water-soluble polar solvent is preferably hexamethylphosphoric triamide.

  According to this, a β-type polyvinylidene fluoride film having superior piezoelectric characteristics and high purity can be reliably produced by a simple method without requiring large-scale equipment.

  Another aspect of the present invention is a β-type polyvinylidene fluoride film produced by applying a coating solution containing polyvinylidene fluoride, comprising granular crystal grains, and the average grain size of the granular crystal grains is The β-type polyvinylidene fluoride film has a volume porosity of 48% to 53%.

  According to this invention, it is possible to realize a β-type polyvinylidene fluoride film having a high volume porosity and excellent porosity in which a plurality of voids exist between crystal grains. Due to the presence of a plurality of voids between the crystal grains, the strain characteristics of the β-type polyvinylidene fluoride film are further improved.

  Another aspect of the present invention is the β-type polyvinylidene fluoride film produced by the method for producing the β-type polyvinylidene fluoride film according to any one of the above aspects, or the β-type polyvinylidene fluoride film according to any one of the above aspects. And an electrode laminated on both sides of the β-type polyvinylidene fluoride film.

  According to the piezoelectric sensor of the present invention, since the β-type polyvinylidene fluoride film having excellent distortion characteristics is provided, a piezoelectric sensor having high sensitivity and stable detection characteristics can be realized.

  Here, the piezoelectric sensor is preferably a piezoelectric hydrogen sensor.

  According to this, since the β-type polyvinylidene fluoride film having excellent distortion characteristics is provided, a piezoelectric hydrogen sensor having high sensitivity and stable detection characteristics can be realized.

  According to the method for producing a β-type polyvinylidene fluoride film of the present invention, a β-type polyvinylidene fluoride film having excellent piezoelectric characteristics and high purity can be produced by a simple method without requiring a large facility. Moreover, according to the β-type polyvinylidene fluoride film of the present invention, a film having excellent porosity in which a plurality of voids exist between crystal grains can be obtained. Thereby, a β-type polyvinylidene fluoride film having excellent strain characteristics can be realized. Furthermore, according to the piezoelectric sensor having such a β-type polyvinylidene fluoride film as a piezoelectric film, a piezoelectric sensor having high sensitivity and stable detection characteristics can be realized.

It is a schematic diagram showing the structure and operating principle of the piezoelectric hydrogen sensor according to the first embodiment. It is a figure which shows the hydrogen gas detection characteristic of Example 1. FIG. It is a figure which shows the hydrogen gas detection characteristic of Example 2. FIG. It is a figure which shows the hydrogen gas detection characteristic of Example 3. It is a figure which shows the hydrogen gas detection characteristic of Example 4. It is a figure which shows the hydrogen gas detection characteristic of Example 5. It is a figure which shows the hydrogen gas detection characteristic of Example 6. It is a figure which shows the hydrogen gas detection characteristic of Example 7. It is a figure which shows the hydrogen gas detection characteristic of Example 8. FIG. 5 is a diagram illustrating hydrogen gas detection characteristics of Comparative Example 1. It is a figure which shows the hydrogen gas detection characteristic of the comparative example 2. 2 is a SEM observation photograph of Example 1 and Comparative Example 1. It is a figure of the absorption spectrum by the infrared spectroscopy of the polyvinylidene fluoride film | membrane of Example 1.

  Hereinafter, the present invention will be described in detail based on embodiments.

(Method for producing β-type polyvinylidene fluoride film)
The method for producing a β-type polyvinylidene fluoride film according to the present invention does not require large-scale equipment, and produces a β-type polyvinylidene fluoride film having excellent piezoelectric characteristics and high purity by a simple method using a solution coating method. is there. In addition, the β-type polyvinylidene fluoride film in the present invention is mainly β-type, and if it exhibits the function as β-type, it also includes a mixture of α-type and the like. It means that the film contains almost no components other than polyvinylidene fluoride.

β-type polyvinylidene fluoride consists of a repeating chain of (—CF ₂ —CH ₂ —) _{n and} a conformation structure in which the molecular chain is all-trans. For this reason, β-type polyvinylidene fluoride has a direction of spontaneous polarization aligned from a fluorine atom to a hydrogen atom, that is, in a direction perpendicular to the molecular chain, and is a material having excellent piezoelectric characteristics.

  The manufacturing method of such a β-type polyvinylidene fluoride film having excellent piezoelectric characteristics is that polyvinylidene fluoride, a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixes it to β-type, and a boiling point that is higher than that of the water-soluble polar solvent. A step of mixing a low organic solvent to form a coating solution, a step of applying the obtained coating solution to a substrate to form a coating film, a step of drying the coating film, and a step of washing the dried film with water The process including these.

  In the present invention, polyvinylidene fluoride is dissolved in a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixed in β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent to obtain a coating solution. After the film formation, the organic solvent is removed to form a porous film, which is washed with water to remove the water-soluble polar solvent, thereby producing a high-purity β-type polyvinylidene fluoride film.

  Hereinafter, each step will be described.

  The coating liquid formation process consists of mixing polyvinylidene fluoride, a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixing it in β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. It is a process to do. Specifically, a polyvinylidene fluoride powder is dissolved in a predetermined water-soluble polar solvent and a predetermined organic solvent to prepare a coating solution containing polyvinylidene fluoride.

  Here, the polyvinylidene fluoride used in the present invention is not only a polymer of vinylidene fluoride alone but also a vinylidene fluoride monomer and fluorine as long as it is a β-type polyvinylidene fluoride film and exhibits piezoelectric characteristics. In the present invention, these are collectively referred to simply as polyvinylidene fluoride. In the present invention, since polyvinylidene fluoride is used after being dissolved in a solvent, it is preferably used in the form of powder, but may be in the form of flakes or lumps.

  Further, the predetermined water-soluble polar solvent used in the present invention has a function of dissolving polyvinylidene fluoride and immobilizing the polyvinylidene fluoride to β-type, such as hexamethylphosphoric triamide (HMPA), etc. And phosphoric acid amide compounds, dimethylacetamide, dimethylformamide, dimethylsulfoxide and the like. The phosphoric acid amide compound includes not only a triamide such as a hexaalkylphosphoric acid triamide but also a monoamide, a diamide, or a mixture thereof. Among these, hexamethyl phosphate triamide is particularly preferable, and hexamethyl phosphate triamide is used in this embodiment.

  Here, the water-soluble polar solvent has the function of immobilizing polyvinylidene fluoride in β-type when the polyvinylidene fluoride is transferred to the β-type crystal structure and immobilized in a state of being compatible with polyvinylidene fluoride. Say. In addition, immobilization to β-type includes not only those that are completely immobilized to β-type, but also those that are fixed so that β-type is superior to α-type. What is necessary is just to fix so that vinylidene may become what has desired piezoelectricity.

  Moreover, the water solubility of a water-soluble polar solvent means water solubility to the extent that it can be removed from a coating film by a water washing step described later.

  The organic solvent having a boiling point lower than that of the water-soluble polar solvent means a solvent having a saturated vapor pressure at a drying temperature described later, which is higher than that of the water-soluble polar solvent and has a high evaporation rate. For this reason, in the drying step of the coating film described later, by heating to about the boiling temperature of the organic solvent, only the organic solvent can be evaporated while the water-soluble polar solvent remains in the coating film. A porous coating film can be obtained. Such an organic solvent is compatible with polyvinylidene fluoride and a water-soluble polar solvent, and may be appropriately selected according to the type of the water-soluble polar solvent to be used.

  Examples of the organic solvent having a boiling point lower than that of the water-soluble polar solvent include acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, dimethylformamide, diethylformamide, dimethylacetamide, diethylacetamide, dimethylbutyramide, and N-methylpyrrolidone. A mixed solvent can be mentioned. Among these, it is preferable to use at least one selected from the group consisting of acetone and dimethylformamide. In the present embodiment, acetone is used in view of easiness of evaporation.

  In the present invention, the coating liquid is formed by mixing the above-mentioned polyvinylidene fluoride, a water-soluble polar solvent that dissolves polyvinylidene fluoride and fixing the β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent. However, the volume ratio of the water-soluble polar solvent and the organic solvent having a boiling point lower than that of the water-soluble polar solvent is particularly limited as long as it can form a coating film that can maintain a porous shape after drying as described above. The organic solvent may be contained in an amount of 10 to 80% by volume. This is because when the organic solvent is less than 10% by volume, a porous film is not formed when the organic solvent is removed, and when it is more than 80% by volume, the shape of the film cannot be maintained. Preferably, the volume ratio of the water-soluble polar solvent to the organic solvent is in the range of 1: 3 to 3: 1.

  The content of polyvinylidene fluoride is preferably in the range of 3.5% by mass or more, and more preferably 5 to 6.5% by mass with respect to the total mass of the water-soluble polar solvent. It is a range.

  More preferably, when hexamethyl phosphate triamide is used as the water-soluble polar solvent, the volume ratio of hexamethyl phosphate triamide to acetone is 1: 1 and the content of polyvinylidene fluoride is hexamethyl phosphate triamide. The total mass is 6.5% by mass.

  In the present invention, the coating solution thus obtained is applied to a substrate to form a coating film. The coating film forming step is a step of forming a coating film by applying a coating solution obtained by mixing to a substrate.

  The coating method is not particularly limited as long as a coating film can be formed. For example, known coating methods such as a spin coating method, a casting method, and an ink jet method can be applied. In the coating process, a desired film thickness can be obtained by increasing the volume (mass) of the coating liquid, increasing the number of coatings, or repeating the coating film forming process and the drying process.

  The substrate is not particularly limited as long as it can hold the coating liquid, and examples thereof include a silicon substrate, a glass substrate, a ceramic substrate, a plastic substrate, a polymer substrate, and a metal substrate. In this embodiment, a glass substrate is used.

  In the present invention, the formed coating film is then dried. The step of drying the coating film is a step of drying the coating film formed on the substrate to form a porous film.

  Specifically, a step of forming a porous dry film by removing only an organic solvent having a boiling point lower than that of a water-soluble polar solvent from a coating film made of a coating liquid containing polyvinylidene fluoride applied on a substrate It is.

  In this embodiment, since acetone is used as the organic solvent, for example, the coating film is heated to about 80 ° C., which is several tens of degrees higher than the boiling point of acetone (about 56 ° C.), and only acetone is evaporated from the coating film. Thus, a dry film is formed.

  In order to remove only the organic solvent from the coating film, the obtained dry film is composed of a predetermined water-soluble polar solvent and polyvinylidene fluoride, and becomes a porous film having a plurality of voids, that is, a porous film. Further, in the dry film, due to the presence of a predetermined water-soluble polar solvent, the direction of spontaneous polarization of the polyvinylidene fluoride film is aligned in a certain direction, and the crystal structure of the film is maintained in the β-type. From the result of the absorption spectrum by infrared spectroscopy described later, it is confirmed that the crystal structure of the polyvinylidene fluoride film contained in the dry film is β-type.

  Examples of the heating device used in the drying process include an RTA (Rapid Thermal Annealing) device that heats by irradiation with an infrared lamp and a hot plate. In this embodiment, a hot plate is used.

  In the present invention, the porous film formed by drying is then washed with water. The water washing step is a step of washing the dried film with water to remove the water-soluble polar solvent. Preferably, the dried film is peeled off from the substrate and washed with water. However, if the water-soluble polar solvent can be removed, the dried film may be washed with water held on the substrate.

  Washing with water may be performed by running water, immersion in water, or the like. In this embodiment, the polyvinylidene fluoride-containing film obtained by drying is peeled off from the substrate, washed with pure water for about 1 minute, and a water-soluble polar solvent such as hexamethylphosphoric triamide in the polyvinylidene fluoride-containing film. Remove.

  Since the dry film becomes a porous film by evaporation of acetone, it is considered that the water-soluble polar solvent, for example, hexamethylphosphoric triamide is removed from the dry film by washing with water. In addition, it was confirmed that the direction of spontaneous polarization of polyvinylidene fluoride was maintained even after removal of water-soluble polar solvent such as hexamethylphosphoric triamide that fixed polyvinylidene fluoride to β-type by washing with water from the dried film Has been. Therefore, a β-type polyvinylidene fluoride film having excellent piezoelectric characteristics and high purity can be formed by washing with water. Also from the result of an absorption spectrum by infrared spectroscopy described later, it is confirmed that the polyvinylidene fluoride film after washing with water is a β-type having a high purity. The film thickness of the formed β-type polyvinylidene fluoride film is about 70 to 300 μm.

  In addition, a porous β-type polyvinylidene fluoride film having a larger volume porosity can be formed by desorption of a predetermined water-soluble polar solvent. Due to the porosity, the polyvinylidene fluoride film has excellent strain characteristics.

  In the present invention, in order to form a β-type polyvinylidene fluoride film having high purity and excellent porosity, an organic solvent having a boiling point lower than that of the water-soluble polar solvent is mixed in the coating solution. In the drying step, the organic solvent is first evaporated while leaving the water-soluble polar solvent in the coating film, so that the remaining film (dry film) is porous. In the subsequent washing step, the organic solvent is dried. A water-soluble polar solvent is further desorbed from the membrane to obtain a more porous membrane. A β-type polyvinylidene fluoride film having high purity and excellent porosity can be formed by the two steps of the drying step and the water washing step.

  Furthermore, according to the production method of the present invention, the porosity of the β-type polyvinylidene fluoride film is changed by changing the mixing ratio of the organic solvent having a boiling point lower than that of the water-soluble polar solvent mixed in the coating solution. It is possible to control the porosity. Specifically, by increasing the mixing ratio of such organic solvents, it is possible to increase the organic solvent that evaporates in the drying step, increase the porosity, and increase the volume porosity.

  As described above, according to the method for producing a β-type polyvinylidene fluoride film according to the present invention, a large-scale facility is not required, and only a coating liquid forming process, a coating film forming process and a drying process, and a dry film washing process are performed. A β-type polyvinylidene fluoride film having excellent piezoelectric characteristics and high purity can be produced by a simple method comprising: In addition, the production of a β-type polyvinylidene fluoride film by such a coating method has a small number of production steps, so that the environmental load is small and the production cost can be reduced. By mounting such a film having excellent piezoelectric characteristics and high purity as a piezoelectric film on various sensors, a sensor having excellent detection characteristics can be realized.

(Β-type polyvinylidene fluoride film)
The β-type polyvinylidene fluoride film according to the present invention is a film made of crystal grains having an average particle diameter of 8 to 9 μm and having a volume porosity of 48 to 53%.

The volume porosity was calculated by the following formula.
Volume porosity (%) = ((mass of true PVDF−mass of apparent PVDF) / mass of true PVDF) × 100
However, the true PVDF mass is a theoretical density of 1.78 g / cm ³ × the volume of the PVDF membrane produced, and the apparent PVDF mass is an actual value measured by a weighing meter.

  Such a polyvinylidene fluoride film is a porous film having a large volume porosity and having a plurality of voids between crystal grains. Due to the presence of these voids, the polyvinylidene fluoride film has excellent strain characteristics. On the other hand, the β-type polyvinylidene fluoride film produced by a conventional stretching method has a flat surface and no granular crystal grains are observed.

  Therefore, the β-type polyvinylidene fluoride film made of granular crystal grains according to the present invention is distinguished from the conventional β-type polyvinylidene fluoride film. For example, the piezoelectric film is used as a piezoelectric sensor for high sensitivity. In addition, a sensor having stable detection characteristics can be realized.

(Piezoelectric sensor)
The piezoelectric sensor according to the present invention uses a β-type polyvinylidene fluoride film manufactured by the above-described manufacturing method or a β-type polyvinylidene fluoride film manufactured by a coating method as a piezoelectric film. In this embodiment, a piezoelectric hydrogen sensor will be described as an example of a piezoelectric sensor.

  FIG. 1 is a schematic diagram showing the structure and operating principle of a piezoelectric hydrogen sensor according to this embodiment. As shown in FIG. 1, the piezoelectric hydrogen sensor 1 includes a pair of palladium electrodes 2 and a β-type polyvinylidene fluoride film 3 sandwiched between the palladium electrodes 2, and both surfaces of the β-type polyvinylidene fluoride film 3. Palladium electrode 2 is formed by laminating palladium. Palladium is a metal that has the property of selectively absorbing only hydrogen and expanding, and is suitable as a piezoelectric hydrogen sensor. Therefore, in the piezoelectric hydrogen sensor 1 according to the present embodiment, when the palladium particles absorb hydrogen existing in the air or the like and expand, the β-type polyvinylidene fluoride film 3 sandwiched between the electrodes is distorted, and β The capacitance of the type polyvinylidene fluoride film 3 changes. This change in capacity is output as a voltage signal to detect hydrogen. Such a piezoelectric hydrogen sensor has a practically important feature that it does not require a power source and operates autonomously at room temperature because it generates a voltage due to distortion of the sensor itself.

  Since the piezoelectric hydrogen sensor 1 according to the present embodiment includes the β-type polyvinylidene fluoride film 3 having excellent strain characteristics, the piezoelectric hydrogen sensor including the β-type polyvinylidene fluoride film formed by the conventional stretching method. For example, although details will be described later, it is known that the output voltage shows a stable potential change and the detection sensitivity is several times better. Thereby, it is possible to realize a highly reliable piezoelectric hydrogen sensor having high sensitivity and stable detection characteristics.

  In addition to piezoelectric hydrogen sensors, β-type polyvinylidene fluoride films having such excellent strain characteristics are widely used in various piezoelectric sensors such as pressure sensors, ultrasonic sensors, acceleration sensors, vibration sensors, and impact sensors. Can be used.

  Hereinafter, based on an Example and a comparative example, it demonstrates still in detail.

Example 1
Table 1 shows the results of the configuration of the coating liquid used in Examples 1 to 8 and Comparative Examples 1 and 2, the film thickness of the polyvinylidene fluoride film, and the detection characteristics of the hydrogen gas sensor implemented in Test Example 1, respectively.

  Based on the above embodiment, 8.30 g (volume ratio 1: 3) of a mixed solution composed of hexamethylphosphoric triamide (hereinafter referred to as “HMPA”) and acetone (purity> 99.5%) was added to β-type polyfluoride. Α-type PVDF powder (manufactured by Polysciences), which is a raw material of vinylidene (hereinafter referred to as “PVDF”), was added to 3.5 mass% (87.0 mg) with respect to the total mass of HMPA, Stirring was performed at about 40 ° C. for about 60 minutes until the PVDF powder was dissolved to obtain a coating solution containing uniform PVDF.

  Next, using the obtained coating solution, 1 to 2.5 ml of the coating solution was applied onto a Petri dish to obtain a PVDF-containing film. Then, the PVDF-containing film applied to the substrate was dried on a hot plate at about 80 ° C. for about 24 hours to obtain a dried film. The obtained dry film was peeled off from the substrate and washed with pure water for about 1 minute to form a PVDF film having a thickness of 130 μm.

A hydrogen sensor was manufactured by forming palladium electrodes with a thickness of 10 nm on both sides of the PVDF membrane. The palladium electrode was formed by DC sputtering.
The crystal structure of the PVDF film was observed using a scanning electron microscope (SEM).
In addition, structural analysis of the PVDF film was performed by infrared spectroscopy.

(Example 2)
In Example 2, an α-type PVDF powder, which is a raw material of PVDF, was added to 4.42 g (volume ratio of 1: 1) of a mixed solution composed of HMPA and acetone at 3.5% by mass with respect to the total mass of HMPA ( 87.0 mg) to obtain a coating solution containing PVDF. Other conditions were the same as in Example 1. In Example 2, a PVDF film having a thickness of 145 μm was formed.

(Example 3)
In Example 3, an α-type PVDF powder, which is a raw material for PVDF, was added to 3.13 g (volume ratio: 3: 1) of a mixed solution composed of HMPA and acetone at 3.5% by mass with respect to the total mass of HMPA ( 87.0 mg) to obtain a coating solution containing PVDF. Other conditions were the same as in Example 1. In Example 3, a PVDF film having a thickness of 195 μm was formed.

Example 4
In Example 4, α-type PVDF powder, which is a raw material of PVDF, was added to 4.42 g (volume ratio 1: 1) of a mixed solution composed of HMPA and acetone at 3% by mass (74.74%) based on the total mass of HMPA. 6 mg), and a coating solution containing PVDF was obtained. Other conditions were the same as in Example 1. In Example 4, a PVDF film having a thickness of 175 μm was formed.

(Example 5)
In Example 5, α-type PVDF powder, which is a raw material of PVDF, was added to 1.77 g (volume ratio 1: 1) of a mixed solution composed of HMPA and acetone at 5 mass% (49.49%) based on the total mass of HMPA. 7 mg), and a coating solution containing PVDF was obtained. Other conditions were the same as in Example 1. In Example 5, a PVDF film having a thickness of 70 μm was formed.

(Example 6)
In Example 6, α-type PVDF powder, which is a raw material of PVDF, was added to 4.42 g (volume ratio 1: 1) of a mixed solution composed of HMPA and acetone at 5% by mass (124.%) with respect to the total mass of HMPA. 3 mg), and a coating solution containing PVDF was obtained. Other conditions were the same as in Example 1. In Example 6, a PVDF film having a thickness of 285 μm was formed.

(Example 7)
In Example 7, an α-type PVDF powder, which is a raw material of PVDF, was added to 1.77 g (volume ratio 1: 1) of a mixed solution composed of HMPA and acetone at 6.5% by mass with respect to the total mass of HMPA ( 64.4 mg) to obtain a coating solution containing PVDF. Other conditions were the same as in Example 1. In Example 7, a PVDF film having a thickness of 70 μm was formed.

(Example 8)
In Example 8, the α-type PVDF powder, which is a raw material of PVDF, was added to 4.42 g (volume ratio 1: 1) of a mixed solution composed of HMPA and acetone at 6.5% by mass with respect to the total mass of HMPA ( 161.5 mg) to obtain a coating solution containing PVDF. Other conditions were the same as in Example 1. In Example 8, a PVDF film having a thickness of 280 μm was formed.

(Comparative Example 1)
In Comparative Example 1, α-type PVDF powder, which is a raw material for β-type PVDF, was added to 2.49 g of HMPA so that the total mass of HMPA was 3.5% by mass (87.0 mg). The conditions other than obtaining the coating solution were the same as in Example 1. The film thickness of the formed PVDF film was 170 μm. Further, the SDF observation was performed on the PVDF film formed in Comparative Example 1 in the same manner as in Example 1.

(Comparative Example 2)
In Comparative Example 2, a commercially available β-type PVDF membrane was used. The film thickness of the commercially available β-type PVDF membrane was 52 μm.

(Test Example 1)
The PVDF film formed based on Examples 1 to 8 and Comparative Examples 1 and 2 was applied as a piezoelectric film to a hydrogen sensor, and the hydrogen gas detection characteristics were evaluated.

  2 to 9 show the results of detection characteristics of the hydrogen sensor including the PVDF film formed based on Examples 1 to 8, respectively.

  10 and 11 show the results of detection characteristics of the hydrogen sensor including the PVDF film formed based on Comparative Examples 1 and 2, respectively.

  Evaluation of the hydrogen gas detection characteristics was performed by installing hydrogen sensors each including the PVDF membranes of Examples 1 to 8 and Comparative Examples 1 and 2 in a cell in which dry air and hydrogen 100% can be alternately introduced. . The operating temperature of the hydrogen sensor was room temperature.

  Table 1 shows the results of detection characteristics of the hydrogen gas sensor. When the output voltage change is extremely large and shows a stable change, ◎, when the output voltage change is large and shows a stable change, ○, when the output voltage change is small or shows a stable change When it did not exist, it was set as x.

  As a result, for the hydrogen sensors of Examples 1 to 3, the amount of change in the output voltage after hydrogen detection showed a large value of about 50 to 60 mV, and for Example 7, a larger value of about 110 mV was shown. Further, Example 8 showed an extremely large value of about 275 mV.

  Even when the hydrogen atmosphere was returned to air, the output voltage of all the sensors of Examples 1-3, 7, and 8 gradually decreased to the initial value. Also, in the hydrogen sensors of Examples 5 and 6, the output voltage after hydrogen detection showed a stable change, and the change amount of the output voltage was about 30 to 35 mV. Also in Example 4, the amount of change in the output voltage was as large as about 55 mV.

  On the other hand, the hydrogen sensor including the PVDF membrane of Comparative Example 1 was not stable because the output voltage fluctuated greatly both after hydrogen detection and after the atmosphere was returned to air. Moreover, about the hydrogen sensor which comprises the commercially available PVDF membrane of Comparative Example 2, the amount of change in the output voltage is only about 10 mV, and the output voltage when the hydrogen atmosphere is returned to the air is the hydrogen sensor of each example. It did not decrease gradually.

  From the above, it has been found that the hydrogen sensor including the β-type polyvinylidene fluoride film according to the present invention is a highly reliable hydrogen sensor having high sensitivity and showing a stable potential change.

(Test Example 2)
The PVDF film formed based on Example 1 and Comparative Example 1 was observed using a scanning electron microscope (SEM). FIG. 12 is a SEM photograph of the PVDF film surface formed based on Example 1 and Comparative Example 1. In addition, the black part of a SEM photograph shows a space | gap.

  As shown in FIG. 12, the PVDF film of Example 1 has a uniform granular crystal grain having an average grain diameter of 8 to 9 μm stacked in a mottled state, and a black showing voids between the crystal grains. It was found that a portion was present throughout the membrane. When the volume porosity was calculated, an extremely large value of 48% to 53% was shown.

  On the other hand, in the PVDF film of Comparative Example 1, it was confirmed that the non-uniform granular crystal grains were in close contact with each other, and the black portions indicating voids were not present in the entire film unlike Example 1. It was done. The volume porosity was calculated to be 30%, indicating a small value.

  Thus, the PVDF film of Example 1 is a porous film having a large volume porosity and having a plurality of voids between crystal grains, and thus has excellent strain characteristics. Actually, the hydrogen sensor comprising the PVDF film of Example 1 as a piezoelectric film exhibits extremely sensitive detection characteristics based on the results of Test Example 1. This is due to the excellent strain characteristics of the β-type PVDF film according to the present invention, and this excellent strain characteristic is due to the presence of a plurality of voids between crystal grains of the β-type PVDF film. is there.

(Test Example 3)
The crystal structure of the PVDF film was analyzed by infrared spectroscopy. As the measuring apparatus, FTA2000 manufactured by ABB-BOMEM was used.

  FIG. 13 shows the result of the absorption spectrum of the PVDF film by infrared spectroscopy. (A) in FIG. 13 shows the absorption spectrum of the dry film after volatilizing acetone from the coating film in Example 1. (B) in FIG. 13 shows the absorption spectrum of the PVDF membrane after removing HMPA in Example 1 by washing the dried membrane with water.

  In (a) of FIG. 13, a plurality of peaks indicating the presence of a β-type PVDF film were observed, and almost no α-type peak was observed. Moreover, the peak of HMPA remaining in the PVDF membrane was observed. In (b) in FIG. 13, these β-type peaks appear sharper. Moreover, since the peak of HMPA was not recognized, it was confirmed that HMPA was removed by washing with water.

  As a result, it was found that in the state where HMPA was contained in the dry film, the peak indicating β-type was weak and the purity of β-type PVDF was low. On the other hand, it was found that by removing HMPA from the dried membrane by washing with water, the peak indicating β-type becomes sharp and the purity of the β-type PVDF membrane increases. Therefore, according to the method for producing a β-type PVDF membrane according to the present invention, a β-type PVDF membrane with extremely high purity can be obtained.

(Other embodiments)
Although one embodiment of the present invention has been described above, the basic configuration of the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the β-type polyvinylidene fluoride film is applied to the piezoelectric hydrogen sensor as a piezoelectric film. However, other than the piezoelectric hydrogen sensor, a pressure sensor, an ultrasonic sensor, an acceleration sensor, a vibration sensor, and an impact sensor are used. It can be widely applied to various sensors. It can also be used for information processing devices such as circuits and software, and output devices such as actuators and transducers.

  INDUSTRIAL APPLICABILITY The present invention can be used in industrial fields such as various sensors, information processing devices, and output devices using the piezoelectric characteristics of β-type polyvinylidene fluoride films.

1 Piezoelectric hydrogen sensor 2 Palladium electrode 3 β-type polyvinylidene fluoride film

Claims (6)

A method for producing a β-type polyvinylidene fluoride film,
Mixing a polyvinylidene fluoride, a water-soluble polar solvent that dissolves the polyvinylidene fluoride and fixing it in β-type, and an organic solvent having a boiling point lower than that of the water-soluble polar solvent to form a coating solution;
A step of applying the obtained coating liquid to a substrate to form a coating film;
Drying the coating film;
And a step of washing the dried membrane with water. A method for producing a β-type polyvinylidene fluoride membrane, comprising: The method for producing a β-type polyvinylidene fluoride film according to claim 1,
The method for producing a β-type polyvinylidene fluoride film, wherein the volume ratio of the water-soluble polar solvent and the organic solvent having a boiling point lower than that of the water-soluble polar solvent is in the range of 1: 3 to 3: 1. In the method for producing a β-type polyvinylidene fluoride film according to claim 1 or 2,
The method for producing a β-type polyvinylidene fluoride film, wherein the water-soluble polar solvent is hexamethylphosphoric triamide. A β-type polyvinylidene fluoride film manufactured by applying a coating liquid containing polyvinylidene fluoride,
Consisting of granular crystal grains,
The average grain size of the granular crystal grains is 8-9 μm,
A β-type polyvinylidene fluoride film having a volume porosity of 48% to 53%. A β-type polyvinylidene fluoride film produced by the method for producing a β-type polyvinylidene fluoride film according to any one of claims 1 to 3, or the β-type polyvinylidene fluoride film according to claim 4,
A piezoelectric sensor comprising electrodes laminated on both sides of the β-type polyvinylidene fluoride film. The piezoelectric sensor according to claim 5, wherein
The piezoelectric sensor is a piezoelectric hydrogen sensor.